The loss of muscle mass and strength in older adults is associated with the appearance of health-risk factors and a reduction in the ability to perform the activities of daily living. An example of this deterioration is a decline in steadiness, documented in hand and arm muscles, but not in large leg muscles. Accordingly, we hypothesize that knee extensor contraction steadiness also declines with age. Strength training is an effective intervention that minimizes these changes, including the decrease in steadiness. Because of the association between declining strength and steadiness, we hypothesize that when older adults train for steadiness, this will be accompanied by an increase in muscle strength. The specific aims of this study are: (1) to assess knee extensor strength and contraction steadiness in young and older adults (2) to compare the strength increases achieved with high-load vs. light-load, steady- contraction training; (3) to determine the effects of strength training on function (4) to identify specific adaptations that contribute to the increase in strength. Young subjects (18-30) will undergo strength and steadiness assessment for comparison with older subjects (65-80), who will be recruited to participate in a 16-week strength-training program. The older subjects will be randomly assigned to one of four experimental groups: Light load-steady contraction, light load (no feedback), heavy load (no feedback), and a control group. The outcome variables will be muscle strength and steadiness, muscle cross-sectional area and volume measured by MRI, temporal (EMG) and spatial (MR-based T2 relaxation time) assessment of muscle activation, coactivation of antagonist muscles, and physical functional performance of the leg muscles. Older subjects will be tested before, and after the training program. This study will provide information on the age-related decline in steadiness of important functional muscles, specific adaptations resulting from an atypical muscle training program, and will likely suggest an alternative intervention to offset the loss of muscle strength in older adults.